Flow-induced vibrations of tubes in two-phase heat exchangers are a concern for the nuclear industry. Electricité de France (EDF) has developed a numerical tool, which allows one to evaluate safety margins and thereafter to optimize the exchanger maintenance policy. The software is based on a semi-analytical model of fluid-dynamic forces and dimensionless fluid force coefficients which need to be evaluated by experiment. A test rig was operated with the aim of assessing parallel triangular tube arrangement submitted to a two-phase vertical cross-flow: a kernel of nine flexible tubes is set in the middle of a rigid bundle. These tubes vibrate as solid bodies (in translation) both in the lift and drag directions in order to represent the so-called in-plane and out-of-plane vibrations. This paper outlines the experimental results and some detailed physical analysis of some selected points of the experiment series: the response modes are identified by means of operational modal analysis (OMA) (i.e., under unmeasured flow excitation) and presented in terms of frequency, damping, and mode shapes. Among all the modes theoretically possible in the bundle, it was found that some of them have a higher response depending on the flow velocity and the void fraction. Mode shapes allow to argue if lock-in is present and to clarify the role of lift and drag forces close to the fluid-elastic instability (FEI).
Operational Modal Analysis of a Triangular-Pitch Tube Bundle Subjected to Two-Phase Cross-Flow
Fluid Mechanics, Energy and
Environment Department (MFEE),
6, quai Watier,
Chatou 78401, France
Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received August 30, 2017; final manuscript received December 8, 2017; published online April 2, 2018. Assoc. Editor: Tomomichi Nakamura.
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Deri, E. (April 2, 2018). "Operational Modal Analysis of a Triangular-Pitch Tube Bundle Subjected to Two-Phase Cross-Flow." ASME. J. Pressure Vessel Technol. June 2018; 140(3): 031301. https://doi.org/10.1115/1.4038725
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